FIG. 11 schematically shows a conventional information reader as positioned in a disk player. As shown in the drawing, a carriage 53 is provided with an optical pickup containing an objective lens 52 for radiating a laser beam onto a recording surface of a disk 51 mounted for rotation about its axis on a disk carrying surface 54 of a turntable 54. The carriage 53 is slidably supported by two laterally spaced guide shafts 55 which are disposed in parallel to the disk-carrying surface 54a of the turntable 54 and which serve as guiding members. A driving means (not shown) is provided to move the carriage 53 in opposite directions as per arrow A.
In the aforementioned information reader 53, the laser beam must be adjusted in two directions with respect to a recording track 51a of the disk 51, that is, the laser beam must be adjusted both in the tangential direction of the recording track and in the radial direction of the disk. Therefore, the carriage 53 or the turntable 54 must be rotatably adjusted relative to each other in the directions of the arrows T and R respectively, corresponding to the tangential and radial directions to thereby adjust the laser beam angular position. For example, the beam angular position is successively adjusted in two directions, or in other words, for example in the case where the adjustment in the direction of the arrow R is made after the adjustment in the direction of the arrow T; the T-direction angular position, once exactly adjusted, shifts out of its normal position again. Accordingly, in the conventional information reader, the adjusting procedure in the two directions must be repeated many times, and consequently, a long time is needed for the adjustment to work. Further, speculative adjustment in which the angular position is adjusted in one direction on speculation as to its divergence in the other direction, has been tried. However, a high degree of skill is required for such speculative adjustment.
For example, a portion of the carriage 53 where the optical pickup is carried is required to be relatively rotatable compared with other portions of the carriage 53, in the directions of the arrows T and R respectively corresponding to the tangential and radial directions. The rotatable portion of the carriage 53 has been designed to be gradually rotated relative to the other, stationary portions thereof by adjusting means to thereby finely adjust the angular position of the laser beam.
In the field of recent disk players for composite disks such as digital audio disks for recording information containing video information, low cost and highly-precise micro-adjustment have been required.
The carriage 53, FIG. 11, is slidably supported by guide shafts 55 which are disposed in parallel to a disk-carrying surface 54a of a turntable 54. A worm such as worm 56 of FIG. 3 may extend along the direction of movement of the carriage 53. The worm 56 is rotationally driven by a driving source. A half nut 53a is provided at a side end portion of the carriage 53 and screwed to the worm 56. In short, the carriage 53 is moved by the rotation of worm 56.
In the aforementioned construction, which, to the extent described may be found in the prior art, it is a basic principle that the guide members such as guide shaft 55 be parallel to the worm 56. If such parallel relation cannot be satisfied at the time of assembly, the worm 56 and the half nut 53a bite into each other obliquely and intensively with the movement of the carriage 53 so that the carriage 53 can lock up. To avoid such a condition, the parallel relation of the guide shaft 55 with the worm 56 must be established with very high precision, and consequently, at increased cost.